Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 211140
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
740 AM EDT Fri Apr 21 2017

.UPDATE...
Issued at 740 AM EDT FRI APR 21 2017

Overnight convection is dissipating and it appears this lull in
activity will continue for the next couple of hours or so.
However, upstream convection is currently moving through western
Kentucky and should be pushing back into our area by mid to late
morning. Frontal boundary has made it as far south as the I-64 and
I-75 corridor to our northwest and continues its slow drift to
the southeast. Main update was to adjust PoPs for the
aforementioned lull. Tweaked Ts and Tds to bring in line with
latest hourly observations. Updated the zone package accordingly.

&&

.SHORT TERM...(Today through Saturday)
Issued at 455 AM EDT FRI APR 21 2017

A cold front has dropped south of the Ohio River this morning,
stretching from roughly CMH southwest to just northwest of LEX to
DYR. This boundary will continue to drift southeastward through
the morning. The GFS stalls this boundary out just south of the
Kentucky-Tennessee state line by this evening. The ECMWF and NAM
are similar but stall the boundary out slightly further north...
possibly by as little as 50-75 miles. There is good agreement
among model solutions, bringing a wave of low pressure eastward
across the TN Valley just south of the Commonwealth through the
day Saturday.

For sensible weather, and with the frontal boundary draped across
the region and more particularly across our southern zones today,
had to keep higher PoPs in place across the southern half of our
forecast area. We will probably see a lull in activity through the
morning, but expect convection to refire along the boundary
through the afternoon with the help of diurnal heating. The front
drifts slightly further south late this afternoon and evening.
Then the wave of low pressure will brings rain back into our area
by late tonight. Rain continues to affect the area through the
remainder of the short term period. Thunder will generally be
restricted to areas along and south of the frontal boundary.

There are considerable differences showing up with respect to
QPF Saturday, with the ECMWF showing some hefty amounts through
the upcoming event. Overall models have not been real consistent
with QPF totals. But with the boundary draped from west to east
across the region and the potential for some training to take
place, we may need to consider some hydro headlines with future
updates. Will pass on concerns to upcoming shifts.

.LONG TERM...(Saturday night through Thursday)
Issued at 455 AM EDT FRI APR 21 2017

The models are in good agreement aloft in the first part of the
extended. This entails a developing closed low descending into the
Tennessee Valley and through Kentucky. This low tracks slowly across
the area this weekend with the GFS reflecting the strongest and
furthest south position while ECMWF and CMC are more northerly -
closer to eastern Kentucky. By Monday morning the upper low will be
passing south and east of the area with the GFS continuing to be the
deepest and furthest south solution - though the ECMWF is similar
while the CMC weaker and more northerly. In fact, the ECMWF and GFS
move the low almost in lock step off the Southeast Coast by Tuesday
morning lending support for the GFS`s more aggressive scenario. For
this feature, will favor the more extreme and classic closed low
solution of the GFS as the ECMWF plays a bit of catch up. Heights
will rebound over Kentucky in the wake of the low while the pattern
becomes more active to the northwest of Kentucky. As it does so,
more energy will brush by the state while broad troughing develops
over the northwest quarter of the country into midweek. This mid
level trough will sharpen up heading into Thursday with an axis over
the desert southwest in the ECMWF and more northerly for the GFS.
This will evolve into a closed low for the ECMWF over the High
Plains on Thursday while the GFS`s version is much further west. The
downstream effects will relate to the strength of a burgeoning ridge
through the Southeast and deep into Kentucky. The model
disagreements during this latter period lowers confidence in the
specifics of the forecast at this time step.

Sensible weather will feature a large sfc low pushing through the
Southern Appalachians as it moves east toward the Atlantic Coast.
This will take its heaviest rains east along with it by Sunday
morning. However, plenty of wrap around lighter rains will follow
through the rest of the weekend and into Monday morning. This
lingering rain, plenty of clouds, and being on the northwest side
of spring sfc low will make for a cool end to the weekend and
slow a temp rebound on Monday. Warmer weather and more sunshine
should arrive in full force Tuesday continuing through the rest of
the upcoming week. As part of this rebound, a warm front lifts
through and becomes active on Wednesday afternoon and evening for
our northern counties with a potential for showers and
thunderstorms. By Thursday, very warm conditions will be in
control of our weather due to ridging aloft and strong high
pressure off to the east resulting in temperatures climbing well
into the 80s.

Made some low temperature adjustments for ridge to valley
distinctions during the latter half of the extended forecast as
we dry out and move out of a weak CAA pattern. As for PoPs, mainly
just enhanced them through Sunday morning as the core of the low
passes through the region.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
ISSUED AT 740 AM EDT FRI APR 21 2017

Overnight convection is dissipating and it appears this lull in
activity will continue for the next couple of hours or so. MVFR
CIGS have developed across the area. These will likely linger
until the next wave of showers and thunderstorms, currently
moving through western Kentucky gets into our area by mid to late
this morning. Kept potential for thunder generally along and south
of the front for the remainder of the day with SME and LOZ being
the two main terminals affected.

A wave of low pressure to our southwest will ride up into the
region later tonight and bring more widespread rain into the
area, eventually dropping flight conditions into IFR territory or
lower just beyond the end of the forecast window. Generally
speaking weather late tonight into Saturday looks less than
favorable for general aviation interests.

Winds will be generally from the west-southwest around 10kts or
less, with some gusts to about 15kts from time to time. Expect
winds to be a bit stronger in the vicinity of any thunderstorms.
Otherwise winds will veer out of the northwest at about 10kts
behind the front as it drops through the area by late tonight.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

UPDATE...RAY
SHORT TERM...RAY
LONG TERM...GREIF
AVIATION...RAY



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